In the Ocean Reef there are many limiting factors. I will only tell about 3 today. 1. If temperture in life zones drop, then more animals than we expected die. 2. If oxygen levels drop, then we no more animals. 3. If we lose our nutrient supplies drop, then animals will starve and die. Dissolved oxygen and water temperature very important limiting factors in aquatic life zones. Oxygen levels, like temperatures, also decrease with depth. Nutrient supplies are usually satisfactory in freshwater ecosystems. However, in open oceans nutrients are often in short supply.